1)当我们谈论一项长期的或习惯性的活动时，用doing形式的情形较多。

How old were you when you first started playing the piano? 你最初弹钢琴的时候有多大？

*比较 She sat down at the piano and started to play. 她在钢琴前坐下开始弹了起来。

2)start 的进行时态之后，不用doing形式。

①I was starting to get angry. 我开始发火了。

②I am starting to cook the dinner. 我正要开始煮饭。

3)在 start 之后出现的动词涉及感情或思想(如 understand, realize等)时，只可用不定式。

①She started to understand what he really wanted. 她开始明白他真正想要什么。

②She started to wonder why he was here. 她开始觉得奇怪为什么他会在这儿。

4)当主语是物不是人时，要用不定式。